Setting up DOSY experiments

Related link: How to minimize DOSY artifacts due to convection

 

1. In Topspin, go to Help -> Manuals, find “DOSY” handout. Read and understand the principle.

2. Decide a suitable d20 (big delta) for your experiment. In edc window, click Experiment. in “…/user” directory, choose experiment DIFFUSION1D. check getprosol box.

3. lock; shim; atma; rga

4. Run a spectrum. This one is with gpz6 = 2 (default; means 2% of the gradient amp power is used).

5. Create a new experiment by edc and choose “Use current parameters“. Don’t do rga. type gpz6 and enter 95 (give the gradient amp 95% of the power). run the experiment.

5a. If the tall peaks have negative spikes on their sides that cannot be fixed by phase correction, type loopadj, then rerun the experiments.

6. compare the two spectra with 2% and 95% gradient powers. if the latter is less than 1% of of the former, you need to reduce d20. If the latter is greater than 10% of the former, you need to increase d20. d20 could range from 0.02 s to 0.5 s. every time you change d20, you need to rerun both experiments.

7. Once an optimal d20 is decided, create another new file by choosing DIFFUSION2D. change d20 to the value that you have determined. enter a suitable NS (should be multiple of 16). enter command dosy 2 95 16 q y y. This is a macro that will run a 2D DOSY expt. Meaning of the parameters: 2: beginning gradient amplitude = 2%; 95: ending gradient amplitude = 95%; 16: number of 1d slices = 16; q: increment is square rooted (alternatively, you could do l for linear increment); the first y: begin acquisition; the second y: do a rga before the run. For more details, please read the Bruker brochure mentioned in step 1.

8. when done, click ProcPars tab and change SI of F1 column to 64. In command line, type xf2 to Fourier transform (only in the 2nd dimension). Correct phase. Read Bruker manual to learn how to phase a 2D spectrum. Only phase-correct rows.

9. type setdiffparm. This sends the experimental parameters that you used to Dynamics Center for data fitting.

10. on main menu, click Analysis -> T1/T2 module -> Dynamics Center. Follow the flow in the new window. Instruction on using Dynamics Center can be found here.

Following is a DOSY spectrum of cyclosoprin-A in benzene-d6. Most peaks are in the upper row while there is only one peak in the lower row. Why?

dosy-cyclosporin